Correlation between immunoreactivity for transglutaminase K and for markers of proliferation and differentiation in normal breast tissue and breast carcinomas

We investigated immunohistochemically localization and expression of transg lutaminase K (TGK) in normal breast tissue (n=10) and in breast carcinomas (n=30). Transglutaminase K was compared with the staining patterns of cytok eratin 10, Ki-67, p53, estrogen and progesterone receptors in these tumors. Weak to strong membrane bound immunoreactivity to TGK was detected in 17 o ut of 30 boast carcinomas analyzed. TGK staining was heterogeneous with vis ual differences between individual tumour cells. Ninety percent of normal b reast tissues revealed no immunoreactivity to TGK. Both intensity of TGK im munostaining and number of TGK-positive cells were upregulated in breast ca rcinomas as compared to normal breast tissue. Analyzing coexpression of TGK with cytokeratin 10, Ki-67, p53, ER and PR, no statistically significant c orrelation was found. Our findings indicate that: (I) TGK is upregulated in breast carcinomas as compared to normal breast tissue. (II) Upregulation o f TGK in breast carcinoma is not exclusively induced by alterations of epit helial differentiation or proliferation, but by different, unknown mechanis ms. (III) Upregulation of TGK in breast carcinomas may play an important ro le in the regulation of tumour cell invasive properties by modulating cell- matrix interactions or by facilitating the assembly of matrix and tissue re modeling.